Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.73   4.561%   $245.436   $245.44   $245.45   $245.40  
  Purchase #2 $50.98   13.297%   $57.7588   $57.76   $57.75   $57.80  
  Purchase #3 $66.63   5.808%   $70.4999   $70.50   $70.50   $70.50  
  Purchase #4 $20.68   10.716%   $22.8961   $22.90   $22.90   $22.90  
  Purchase #5 $238.33   13.328%   $270.0946   $270.09   $270.10   $270.10  
  Purchase #6 $31.39   12.395%   $35.2808   $35.28   $35.30   $35.30  
  Purchase #7 $56.32   8.306%   $60.9979   $61.00   $61.00   $61.00  
  7 purchase totals = $699.06       $762.9641   $762.97   $763.00   $763.00